1. Field of the Invention
The present invention relates generally to electric control apparatus for controlling equipment, and more particularly to electric control apparatus having an electric circuit including a circuit element functionable within a specified range of working voltage, such as a digital integrated circuit ("IC").
2. Description of Relevant Art
In general, vehicles are equipped with various devices adapted to be driven with a drive signal depending on the traveling state, such as, for example, a fuel injector. The drive signal of such equipment is generated by electric control apparatus, at a drive circuit therein consisting of various integrated circuits ("ICs"), such as a CPU and a counter, which cooperate with each other to give the drive signal in dependence on various parameters representing the traveling state of vehicle, such as the vehicle speed, suction pressure in the intake pipe of engine, and temperature of radiator cooling water.
Such ICs as the CPU and the counter generally have a specified range of working voltage in which they can normally operate. If the supply voltage is varied lower than the lower limit of the working voltage range, the ICs are unable to operate normally, entering what is called an unstable state in which they have unstable outputs. Accordingly, the drive circuit in electric control apparatus to which power is applied from a vehicle-mounted battery fails to operate normally when the supply voltage is lowered below the lower limit of the working voltage range for a certain reason, so that the injector is unable to function.
Conventionally, it has been usual to interrupt the supply of the drive signal from the drive circuit to the injector to thereby avoid what is called a gasoline lock condition in which the injector is left open as it is injecting gasoline, when the supply voltage is lowered below the lower limit of the working voltage range. Namely, there has been employed a breaking circuit for interrupting the signal transmission from the drive circuit to the injector when the supply voltage to the drive circuit is detected to be lower than the lower limit of the working voltage range.
In this respect, if such breaking circuit has been constituted with ICs having the same working voltage range as the ICs of the drive circuit, the expected effect could not have been given. Such ICs as employed in the breaking circuit have been selected from ICs having a working voltage range with a lower limit under the lower limit of the working voltage range of the ICs constituting the drive circuit.
However, even by the provision of such consideration in the IC selection of the breaking circuit the above effect thereof can not be expected when the supply voltage is lowered below the lower limit of the working voltage range of thus selected ICs of the breaking circuit. Moreover, in such selection of ICs for the breaking circuit, the number of selectable ICs has to be limited in additional to the long time and labor needed for optimum selection, thus resulting in an increased production cost.
The present invention has been achieved to effectively solve such problems in conventional electric control apparatus for equipment.